Tubular anodes are widely used in cathodic protection and may be formed of a variety of material such as high silicon cast iron, graphite, carbon, magnetite, steel etc. When formed of metal such as the noted cast iron, the tubular anodes are normally centrifugally cast.
Internal electrical connections for such anodes may include a wire lead extending from one end or both ends. Such anodes are often times connected together in a string or series and electrically interconnected requiring a double-ended connection.
In practice, although there is usually not supposed to be any tension or pull on the wire lead, such tension is sometimes unavoidable in the construction, shipping or installation of the anode. It is thus important that tension on the wire lead from either end of the anode not exert a force which would tend to loosen or disconnect the lead from the anode.
Wedge connections have been widely employed for tubular anodes and such connections usually take the form of a lead plate or other center cone which is driven into and forms a lead or other soft metal ring or collet surrounding the center plate. The center plate may be in the form of a cone or a star-shaped plate to which the wire lead is cast and the plate is then driven into the outer ring which may deform both the center plate and the ring.
One principle problem with such connections is that lead oxide may form on the components and that lead oxide is a complete insulator. Accordingly, it would be an advantage not to use lead which is now commonly employed.
Lead also acts as a heat sink when heated or if soldering, welding or brazing or hot sealant is employed, and this contributes to the formation of the oxide. Moreover, it has to be cooled before installation of the anode.
Also such connections are extremely difficult to form with any consistent desired low level of resistance. If such connections fail to pass a resistivity test, sometimes the entire assembly must be scrapped including the expensive anodes. Also, while a pull on a wire lead in one direction may tend to tighten the wedge connection, a pull on a wire lead extending in the opposite direction would tend to pull the wedge apart. Moreover, such double-ended connections are extremely difficult to form.
Also complicating the formation of prior art lead wedge connections is the requirement for complex assembly tools and a heating of the materials employed to attach a lead wire to the connector as by welding, casting or brazing.
Such leaded connections are, moreover, impractical if the connection has to be made in the field. The heat and special tools make the job very laborious and the connection unreliable. Also, lead tends to be bent out of shape and can't be reused.
It should also be noted that if the connection completely blocks the interior of the anode as many wedge ring types do, it is then more difficult to seal the connection inside the anode. The sealing material would then have to be poured into the anode from opposite ends and this is a time consuming and cumbersome task, particularly with long anodes.
It is therefore important to provide an electrical connection for such anodes which can quickly and easily be made and which will provide an assured consistency of low resistivity. It is also important that the connection be inexpensive and readily used with either single or double end connections, with a pull on the wire lead from either direction simply further tightening the connection.